As is known, lysozyme is a natural protein found in biological fluids which has an enzymatic activity and a marked lytic action on various saprophytic and pathogenic bacteria. From a biological point of view, it has a defensive role, i.e. it can protect the organism from attack by pathogenic viral and bacterial mecroorganisms and, as such, lysozyme is considered to be an endogenous antibiotic.
The structure of lysozyme has been completely elucidated; it consists of 129 amino acid residues, the radicals of dibasic amino acids being particularly abundant, there being 11 residues of arginine, six residues of lysine and one of histidine. This particular composition of lysozyme gives it a strong positive charge and a high isoelectric point (around 11), which differentiates it from the majority of the other proteins, in which the acidic character generally prevails.
In view of the biological interest connected with the basic properties of lysozyme, numerous derivatives of lysozyme have also been prepared, these having an even higher positive charge than lysozyme itself. Some of these derivatives (see British Patent Specification No. 1,209,214) are obtained, for example, by blocking the acid functions of the dicarboxylic amino acid residues (aspartic acid and glutamic acid) by esterification or by converting the .epsilon.-amino-groups of the lysine radicals into the more basic .epsilon.-guanidino-groups to give radicals of homoarginine or by using both procedures.
Biologically, all the above derivatives retain or enhance the antiviral activity of the original lysozyme on the RNA- and the DNA-viruses and are able to form complexes with them by neutralisation of the opposite charges, with consequent precipitation. The guanidyl-lysozymes also retain the typical anti-bacterial lytic activity of lysozyme.
The above-described properties enable lysozyme and its more basic derivatives to form water-soluble salts with strong acids, for example hydrochloric acid, as well as with weak acids, for example ascorbic acid. Lysozyme and its basic derivatives also have a marked tendency to form complexes, which are generally insoluble, with many anionic macromolecules, for example with nucleic acids and with electronegative colloids.